This study will investigate differences between a premixed insulin preparation containing 5 units NPH for every 5 units regular insulin (50/50) and a (70/30) insulin preparation. Two 12 hour euglycemic clamp procedures will be performed in healthy men. Subjects will receive 0.2 units subcutaneously of the 50/50 or 70/30 insulin preparation in a blinded manner. Twenty percent dextrose will be infused at a dose titrated to maintain euglycemia. The primary efficacy measure will be the difference in glucose infusion rates required to maintain euglycemia during the first 4 hours after injection.